Composite materials are used to replace metal in many applications. For example, composite materials are used is in the fabrication of tubulars, such as pipes and pipelines used in oilfield exploration, drilling and production operations.
The construction of composite tubulars may take a variety of forms, depending upon the intended application of the tubular. Generally, composite tubulars comprise a plurality of layers of material, the selection of the layers being determined by the intended application. Wolfe et al. U.S. Pat. No. 5,261,462 and Wolfe et al. U.S. Pat. No. 5,435,867 disclose a tubular structure such as a pipe or a pressure vessel. Commonly, the composite pipes are prepared by winding the fibers impregnated with epoxy resin using a filament winding process around a mandrel. The filaments can be carbon fiber or other types of materials. As an alternative, if it is required to have a metallic liner present in the finished pipe, the filament winding process may be carried out around the liner itself. The epoxy is allowed to cure in order to complete the composite structure. The selection of the materials, the number, arrangement and thickness of the individual layers, together with the orientation of the fibers in the individual layers, are determined by the type of application.
During construction of composite tubulars, sagging and bending of the mandrel can result in unwanted flexing and wrinkling of the uncured composite. This is especially true when a long, slender mandrel is used to fabricate very long tubulars having small diameters.
Several different approaches have been taken to address the problems associated with sagging and bending of the filament winding mandrel. For example, special filament winding machines that apply tension and/or a bending moment to the ends of the mandrel have been used in an effort to prevent sagging in the mandrel. These special filament winding machines are expensive, requiring significant support structure and bearings. Another approach to avoid sagging or bending in the mandrel has been to inflate or pressurize the entire interior length of the mandrel. However, pressurizing the entire interior length of mandrel, which is typically metallic, is potentially dangerous to workers. This is because the significant volume presented by the mandrel's interior results in a large amount of stored energy in the pressurized mandrel, thereby increasing the destructive potential if the mandrel ruptures. Still another approach has been the use of rollers to support the mandrel during the filament winding process. Although the rollers may prevent sagging and bending, the rollers pinch and contaminate the uncured composite.
The fabrication of quality long, slender composite tubulars requires that mandrel sagging and bending be controlled. Current methods are expensive or do not prevent the unwanted wrinkling or contamination of the uncured resin. A need exists for a technique to control the sagging and bending in the filament winding mandrel in a cost-effective manner.